Using some kind of unit of measurement for scale?
In fact Blender could be switched to Metrics or Imperials using menu shown below...



...in my case, every single "rectangle" of the grey grid is one square metre. After switching to this You will be able to simply put the EXACT data in the "N" menu (right one) of your ViewPort where the Location or Size is (Location could be seen on the picture).

Hope it helps buddy, Jan.